<!DOCTYPE html>
<title>CSS Positioned Layout Module Test: 'overlay' is transitioned in and out of 'auto'</title>
<link rel="help" href="https://drafts.csswg.org/css-position-4/#overlay">
<link rel="help" href="https://html.spec.whatwg.org/multipage/popover.html">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
  #transition-in, #transition-out {
    /* Force display:block both popover open or closed to not rely on
       @starting-style or display transitions. */
    display: block;
  }
  .enable-transitions :is(#transition-in, #transition-out) {
    transition: overlay 60s step-end;
    transition-behavior: allow-discrete;
  }
</style>
<div id="container">
  <div id="transition-in" popover></div>
  <div id="transition-out" popover></div>
</div>
<script>
  let transition_in = document.querySelector("#transition-in");
  let transition_out = document.querySelector("#transition-out");

  test(() => {
    transition_out.showPopover();
    assert_equals(getComputedStyle(transition_in).overlay, "none");
    assert_equals(getComputedStyle(transition_out).overlay, "auto");
  }, "Open the popover to be closed and verify computed overlay for both popovers");

  container.className = "enable-transitions";

  test(() => {
    assert_true(transition_out.matches(':popover-open'));
    assert_false(transition_in.matches(':popover-open'));
    transition_in.showPopover();
    assert_true(transition_in.matches(':popover-open'));
    assert_false(transition_out.matches(':popover-open'));
    assert_equals(getComputedStyle(transition_in).overlay, "none",
       'Transition in should be delayed');
    assert_equals(getComputedStyle(transition_out).overlay, "auto",
       'Transition out should be delayed');
  }, "Transition overlays");
</script>
